The objective of this program is to develop new radiolabeled pharmaceuticals whose chemical, immunologic and biologic properties are well defined in relation to the parent compound. This will be achieved by chromatographic analyses, antibody competitive binding assays, in vitro bioassays and biological distribution in animals. The successful preparation of such compounds will result in agents which are capable of measuring a specific biologic function. The proposed approach using known biologically active compounds seems especially applicable to the hormone related diseases.